1. Field of the Invention
The present invention relates to a communication system, a communication method and a program, and more particularly to a communication system and a communication method suitable for use in communicating with communication terminals in which a communication technique using a human body as a communication medium is applied.
2. Description of Related Art
In a communication system formed with a transmitter, a communication medium and a receiver, communication has heretofore been established by a physical communication signal transmission path for transmitting communication signals and a physical reference point provided separately from the communication signal transmission path so that a reference point for determining the difference in level between communication signals is shared by the transmitter and the receiver (refer to, for example, Japanese Patent Application Publication Number H10-229357 and Japanese Translation of PCT Patent Application Number H11-509380).
For example, in each of the patent applications, a description is given as to communication techniques using a human body as a communication medium. In either of the methods, not only is a first communication path provided as a human body, but also the direct capacitive coupling between electrodes on the ground or in space is provided as a second communication path so that the entire communication path made of the first communication path and the second communication path forms a closed circuit;
In the communication system, two communication paths, i.e., a communication signal transmission path and a reference point path (a first communication path and a second communication path), need to be provided as a closed circuit between the transmitter and the receiver. However, since both communication paths are mutually different paths, these two communication paths must be stably compatible, so that there is a risk of restricting use environments for communications.
For example, the strength of capacitive coupling between the transmitter and the receiver on the reference point path depends on the distance between the devices, and the stability of the communication path varies with the distance. Namely, in this case, there is a risk that the stability of communication depends on the distance between the transmitter and the receiver. In addition, there is a risk that the stability of communication varies according to the presence or absence of a shield or the like between the transmitter and the receiver.
Accordingly, in the communication methods of forming two communication paths, i.e., the communication signal transmission path and the reference point path, as a closed circuit, since use environments greatly influence the stability of communication, stable communication is difficult to perform.